(a) Technical Field
The present disclosure relates to a novel piperazinium trifluoroacetate compound and a carbon dioxide absorbent comprising the same.
(b) Background Art
Various methods such as absorption, adsorption, membrane separation, and cryogenic separation are used to separate carbon dioxide from exhaust gas of chemical plants, power plants or large-sized boilers and from natural gas. An absorption or adsorption method is widely used when the concentration of exhausted carbon dioxide is low. The method is industrially used since it can selectively separate a particular gas that can be well absorbed or adsorbed into an absorbent or adsorbent; however, since the absorbent or adsorbent becomes chemically and/or physically inactivated during the separation, it is necessary to periodically replace the absorbent or adsorbent.
An absorption method in which a liquid absorbent is used is widely used in purification of a large amount of exhaust gas or used in gas separation since it is easy to replace the absorbent; however, the liquid absorbent may be chemically and/or physically inactivated.
As carbon dioxide absorbents, amine solutions such as monoethanolamine (MEA), N-methyldiethanolamine (MDEA), diethanolamine (DEA), etc., are widely used since the amine absorbent is chemically combined with carbon dioxide and, when heat is applied thereto, the chemical bond between carbon dioxide and the absorbent is broken such that the carbon dioxide can be stripped and recovered and the absorbent can be recycled. However, this process has several problems such as irreversible decomposition of amine due to high temperature used to break up the chemical bond between carbon dioxide and the absorbent during the recycling process of the absorbent, replenishment of the absorbent, corrosion of an absorption device by amine itself or decomposition products, and contamination of gas recycled by the vapor pressure of the absorbent.
There have been reported various methods of physically absorbing carbon dioxide using organic solvents such as Selexol, IFPexol, NFM, etc. One advantage of the organic solvent absorbents over the aqueous amine absorbents is that there is required a lower energy to recover carbon dioxide and recycle solvents since the absorption of carbon dioxide is achieved by a physical interaction between the solvent and carbon dioxide, not by the chemical bond as in the case of the aqueous amine absorbents. More specifically, in case of the amine absorbent, the recovery of carbon dioxide and the recycling of solvent require an energy-intensive high-temperature stripping process; on the other hand, in case of the physical absorption, it is possible to recover carbon dioxide dissolved in the solvent by simply changing the pressure, not by increasing the temperature.
Nevertheless, the physical absorption method has some drawbacks. For example, since the organic solvent exhibits a carbon dioxide absorption capacity significantly lower than that of an aqueous amine solution, the circulation rate of the absorbent is high, thus necessitating a relatively larger equipment. In addition, since the physical absorption process by the organic solvent requires an absorbent circulation rate much higher than that of the aqueous amine solution, a larger capital and a higher equipment cost are required. Further, since the solvent used in the physical absorption process has a low boiling point, it tends to be lost during the absorption and recycling process.
Various attempts have been made to use as an absorbent a non-volatile ionic liquid having a high thermal stability and maintaining its liquid phase at a low temperature below 100° C., as disclosed in U.S. Pat. No. 6,849,774 B2, U.S. Pat. No. 6,623,659 B2, and U.S. Patent Publication No. 20080146849 A1. The ionic liquid is a salt compound having a polarity and containing an organic cation and an organic or inorganic anion. The solubility of gas absorbed into the ionic liquid varies according to the degree of interaction between the gas and ionic liquid. Therefore, if the polarity, acidity, basicity, and nucleophilicity of the ionic liquid are changed by appropriately changing the cation and anion structures of the ionic liquid, it is possible to adjust the solubility of a specific gas to some extent.
Typically, ionic liquids absorbents contain nitrogen-containing organic cations such as quaternary ammonium including imidazolium, pyrazolium, triazolium, pyridinium, pyridazinium, and pyrimidinium, and anions such as halogens (e.g., Cl−, Br−, and I−), BF4−, PF6−, (CF3SO)2N−, CF3SO3−, MeSO3−, NO3−, CF3CO2−, and CH3CO2−. Especially, it is reported that an anion containing a fluorine atom has a relatively high carbon dioxide absorption capacity. However, these ionic liquid absorbents have problems that the carbon dioxide absorption capacity is significantly low or their manufacturing cost is very high compared to the amine absorbents, thus lowering the economic efficiency.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.